1. Field of the Invention
The present invention relates to modules for liquid electrolyte, electric energy storing devices, such as batteries. More particularly, the present invention relates to a module for an aqueous battery system wherein the system includes liquid electrolyte batteries and reservoirs for holding liquid electrolyte.
2. Description of the Prior Art
Present liquid electrolyte battery systems include batteries coupled in fluid-flowing relation to external reservoirs. The reservoirs hold electrolyte which is cycled to the battery to support the charge and discharge reactions. The electrolyte contains one or more chemical reactants. For example, in a flowing electrolyte, zinc-bromine battery, aqueous zinc-bromine and quaternary ammonium salts, for example, methylethylpyrrolidinium bromide, with optional supporting salts, such as NH.sub.4 Cl, is circulated to the battery from external reservoirs.
Internally, the batteries include a stack of cells which is made from a series of alternating electrodes and ion-permeable separators. In bipolar, zinc-bromine batteries each cell includes a bipolar electrode upon which an anodic reaction and a cathodic reaction occurs. For purposes of discussion, the anodic side of the bipolar electrode is called an anode, and the cathodic side of the bipolar electrode is called a cathode.
While the battery is charged, the following chemical reaction takes place: EQU Zn.sup.++ +2e.sup.- .fwdarw.Zn EQU 2Br.sup.- .fwdarw.Br+2e.sup.-
Zinc is plated on the anode, and bromine is evolved on the cathode. The bromine is immediately complexed by quaternary ammonium ions in the electrolyte to form a dense second phase which is removed from the battery stack with the flowing electrolyte. The complexed bromine is stored in a catholyte reservoir. The bromine evolved during the reaction is complexed in order to lower its chemical reactivity. However, the complexed bromine is still a relatively hazardous and caustic material.
While the battery is discharged, the following reaction takes place: EQU Br.sub.2 +2e.sup.- .fwdarw.2 Br.sup.- EQU Zn.fwdarw.Zn.sup.++ +2e.sup.-
Zinc is oxidized and the released electrons pass through the electrode where they combine with molecular bromine to form bromine ions. Positively charged zinc ions travel through the separator and remain in solution, and at the same time, negatively charged bromine ions pass through the separator in the opposite direction and remain in solution.
As should be apparent, one important objective in liquid electrolyte battery design is to prevent and minimize the effects of electrolyte leaks. Present techniques for containing bromine leaks in zinc-bromine batteries include placing the reservoirs, batteries, and plumbing (which connects the reservoirs to the batteries) within a spill tray. The spill tray also acts as a module in which all the components are mounted and by which they may be moved as a complete, portable system.
However, when placed in a spill tray, the components of a flow battery are all exposed to the environment. Accordingly, liquid bromine, and bromine gas formed from liquid bromine, may still escape from the system, thereby creating a hazard to people and the environment.
In addition, the spill tray technique of integrating batteries, reservoirs, and plumbing into a system is inadequate because it does not include any means for minimizing the results of a reservoir puncture which may occur, for example, while battery modules are transported or otherwise handled.
Accordingly, it would be desirable to have an improved module for supporting and containing the components of an operational, flowing electrolyte battery. Those components include the batteries, electrolyte containing reservoirs, and plumbing connecting the reservoirs and batteries. In addition, it would be desirable to have an improved module which contains substantially more gaseous bromine from bromide leaks than prior-art devices, and which has a means for minimizing, or is designed to minimize, the results of physical punctures to the reservoirs of the battery.